JOSE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track May 28, 2013
Expires: November 29, 2013
JSON Web Algorithms (JWA)draft-ietf-jose-json-web-algorithms-11
Abstract
The JSON Web Algorithms (JWA) specification enumerates cryptographic
algorithms and identifiers to be used with the JSON Web Signature
(JWS), JSON Web Encryption (JWE), and JSON Web Key (JWK)
specifications.
Status of this Memo
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Internet-Draft JSON Web Algorithms (JWA) May 20131. Introduction
The JSON Web Algorithms (JWA) specification enumerates cryptographic
algorithms and identifiers to be used with the JSON Web Signature
(JWS) [JWS], JSON Web Encryption (JWE) [JWE], and JSON Web Key (JWK)
[JWK] specifications. All these specifications utilize JavaScript
Object Notation (JSON) [RFC4627] based data structures. This
specification also describes the semantics and operations that are
specific to these algorithms and key types.
Enumerating the algorithms and identifiers for them in this
specification, rather than in the JWS, JWE, and JWK specifications,
is intended to allow them to remain unchanged in the face of changes
in the set of required, recommended, optional, and deprecated
algorithms over time.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in Key words for use in
RFCs to Indicate Requirement Levels [RFC2119].
2. Terminology2.1. Terms Incorporated from the JWS Specification
These terms defined by the JSON Web Signature (JWS) [JWS]
specification are incorporated into this specification:
JSON Web Signature (JWS) A data structure representing a digitally
signed or MACed message. The structure represents three values:
the JWS Header, the JWS Payload, and the JWS Signature.
JSON Text Object A UTF-8 [RFC3629] encoded text string representing
a JSON object; the syntax of JSON objects is defined in Section2.2 of [RFC4627].
JWS Header A JSON Text Object (or JSON Text Objects, when using the
JWS JSON Serialization) that describes the digital signature or
MAC operation applied to create the JWS Signature value. The
members of the JWS Header object(s) are Header Parameters.
JWS Payload The sequence of octets to be secured -- a.k.a., the
message. The payload can contain an arbitrary sequence of octets.
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JWS Signature A sequence of octets containing the cryptographic
material that ensures the integrity of the JWS Protected Header
and the JWS Payload. The JWS Signature value is a digital
signature or MAC value calculated over the JWS Signing Input using
the parameters specified in the JWS Header.
JWS Protected Header A JSON Text Object that contains the portion of
the JWS Header that is integrity protected. For the JWS Compact
Serialization, this comprises the entire JWS Header. For the JWS
JSON Serialization, this is one component of the JWS Header.
Base64url Encoding The URL- and filename-safe Base64 encoding
described in RFC 4648[RFC4648], Section 5, with the (non URL-
safe) '=' padding characters omitted, as permitted by Section 3.2.
(See Appendix C of [JWS] for notes on implementing base64url
encoding without padding.)
Encoded JWS Header Base64url encoding of the JWS Protected Header.
Encoded JWS Payload Base64url encoding of the JWS Payload.
Encoded JWS Signature Base64url encoding of the JWS Signature.
JWS Signing Input The concatenation of the Encoded JWS Header, a
period ('.') character, and the Encoded JWS Payload.
Collision Resistant Namespace A namespace that allows names to be
allocated in a manner such that they are highly unlikely to
collide with other names. For instance, collision resistance can
be achieved through administrative delegation of portions of the
namespace or through use of collision-resistant name allocation
functions. Examples of Collision Resistant Namespaces include:
Domain Names, Object Identifiers (OIDs) as defined in the ITU-T
X.660 and X.670 Recommendation series, and Universally Unique
IDentifiers (UUIDs) [RFC4122]. When using an administratively
delegated namespace, the definer of a name needs to take
reasonable precautions to ensure they are in control of the
portion of the namespace they use to define the name.
2.2. Terms Incorporated from the JWE Specification
These terms defined by the JSON Web Encryption (JWE) [JWE]
specification are incorporated into this specification:
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JSON Web Encryption (JWE) A data structure representing an encrypted
message. The structure represents five values: the JWE Header,
the JWE Encrypted Key, the JWE Initialization Vector, the JWE
Ciphertext, and the JWE Authentication Tag.
Authenticated Encryption An Authenticated Encryption algorithm is
one that provides an integrated content integrity check.
Authenticated Encryption algorithms accept two inputs, the
Plaintext and the Additional Authenticated Data value, and produce
two outputs, the Ciphertext and the Authentication Tag value. AES
Galois/Counter Mode (GCM) is one such algorithm.
Plaintext The sequence of octets to be encrypted -- a.k.a., the
message. The plaintext can contain an arbitrary sequence of
octets.
Ciphertext An encrypted representation of the Plaintext.
Additional Authenticated Data (AAD) An input to an Authenticated
Encryption operation that is integrity protected but not
encrypted.
Authentication Tag An output of an Authenticated Encryption
operation that ensures the integrity of the Ciphertext and the
Additional Authenticated Data. Note that some algorithms may not
use an Authentication Tag, in which case this value is the empty
octet sequence.
Content Encryption Key (CEK) A symmetric key for the Authenticated
Encryption algorithm used to encrypt the Plaintext for the
recipient to produce the Ciphertext and the Authentication Tag.
JWE Header A JSON Text Object (or JSON Text Objects, when using the
JWE JSON Serialization) that describes the encryption operations
applied to create the JWE Encrypted Key, the JWE Ciphertext, and
the JWE Authentication Tag. The members of the JWE Header
object(s) are Header Parameters.
JWE Encrypted Key The result of encrypting the Content Encryption
Key (CEK) with the intended recipient's key using the specified
algorithm. Note that for some algorithms, the JWE Encrypted Key
value is specified as being the empty octet sequence.
JWE Initialization Vector A sequence of octets containing the
Initialization Vector used when encrypting the Plaintext. Note
that some algorithms may not use an Initialization Vector, in
which case this value is the empty octet sequence.
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JWE Ciphertext A sequence of octets containing the Ciphertext for a
JWE.
JWE Authentication Tag A sequence of octets containing the
Authentication Tag for a JWE.
JWE Protected Header A JSON Text Object that contains the portion of
the JWE Header that is integrity protected. For the JWE Compact
Serialization, this comprises the entire JWE Header. For the JWE
JSON Serialization, this is one component of the JWE Header.
Encoded JWE Header Base64url encoding of the JWE Protected Header.
Encoded JWE Encrypted Key Base64url encoding of the JWE Encrypted
Key.
Encoded JWE Initialization Vector Base64url encoding of the JWE
Initialization Vector.
Encoded JWE Ciphertext Base64url encoding of the JWE Ciphertext.
Encoded JWE Authentication Tag Base64url encoding of the JWE
Authentication Tag.
Key Management Mode A method of determining the Content Encryption
Key (CEK) value to use. Each algorithm used for determining the
CEK value uses a specific Key Management Mode. Key Management
Modes employed by this specification are Key Encryption, Key
Wrapping, Direct Key Agreement, Key Agreement with Key Wrapping,
and Direct Encryption.
Key Encryption A Key Management Mode in which the Content Encryption
Key (CEK) value is encrypted to the intended recipient using an
asymmetric encryption algorithm.
Key Wrapping A Key Management Mode in which the Content Encryption
Key (CEK) value is encrypted to the intended recipient using a
symmetric key wrapping algorithm.
Direct Key Agreement A Key Management Mode in which a key agreement
algorithm is used to agree upon the Content Encryption Key (CEK)
value.
Key Agreement with Key Wrapping A Key Management Mode in which a key
agreement algorithm is used to agree upon a symmetric key used to
encrypt the Content Encryption Key (CEK) value to the intended
recipient using a symmetric key wrapping algorithm.
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Direct Encryption A Key Management Mode in which the Content
Encryption Key (CEK) value used is the secret symmetric key value
shared between the parties.
2.3. Terms Incorporated from the JWK Specification
These terms defined by the JSON Web Key (JWK) [JWK] specification are
incorporated into this specification:
JSON Web Key (JWK) A JSON object that represents a cryptographic
key.
JSON Web Key Set (JWK Set) A JSON object that contains an array of
JWKs as the value of its "keys" member.
2.4. Defined Terms
These terms are defined for use by this specification:
Header Parameter A name/value pair that is member of a JWS Header or
JWE Header.
Header Parameter Name The name of a member of a JSON object
representing a JWS Header or JWE Header.
Header Parameter Value The value of a member of a JSON object
representing a JWS Header or JWE Header.
3. Cryptographic Algorithms for JWS
JWS uses cryptographic algorithms to digitally sign or create a
Message Authentication Codes (MAC) of the contents of the JWS Header
and the JWS Payload. The use of the following algorithms for
producing JWSs is defined in this section.
3.1. "alg" (Algorithm) Header Parameter Values for JWS
The table below is the set of "alg" (algorithm) header parameter
values defined by this specification for use with JWS, each of which
is explained in more detail in the following sections:
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which therefore demonstrates that whoever generated the MAC was in
possession of the secret. The means of exchanging the shared key is
outside the scope of this specification.
The algorithm for implementing and validating HMACs is provided in
RFC 2104 [RFC2104]. This section defines the use of the HMAC SHA-
256, HMAC SHA-384, and HMAC SHA-512 functions [SHS]. The "alg"
(algorithm) header parameter values "HS256", "HS384", and "HS512" are
used in the JWS Header to indicate that the Encoded JWS Signature
contains a base64url encoded HMAC value using the respective hash
function.
A key of the same size as the hash output (for instance, 256 bits for
"HS256") or larger MUST be used with this algorithm.
The HMAC SHA-256 MAC is generated per RFC 2104, using SHA-256 as the
hash algorithm "H", using the octets of the ASCII [USASCII]
representation of the JWS Signing Input as the "text" value, and
using the shared key. The HMAC output value is the JWS Signature.
The JWS signature is base64url encoded to produce the Encoded JWS
Signature.
The HMAC SHA-256 MAC for a JWS is validated by computing an HMAC
value per RFC 2104, using SHA-256 as the hash algorithm "H", using
the octets of the ASCII representation of the received JWS Signing
Input as the "text" value, and using the shared key. This computed
HMAC value is then compared to the result of base64url decoding the
received Encoded JWS signature. Alternatively, the computed HMAC
value can be base64url encoded and compared to the received Encoded
JWS Signature, as this comparison produces the same result as
comparing the unencoded values. In either case, if the values match,
the HMAC has been validated. If the validation fails, the JWS MUST
be rejected.
Securing content with the HMAC SHA-384 and HMAC SHA-512 algorithms is
performed identically to the procedure for HMAC SHA-256 - just using
the corresponding hash algorithm with correspondingly larger minimum
key sizes and result values: 384 bits each for HMAC SHA-384 and 512
bits each for HMAC SHA-512.
An example using this algorithm is shown in Appendix A.1 of [JWS].
3.3. Digital Signature with RSASSA-PKCS1-V1_5 and SHA-256, SHA-384, or SHA-512
This section defines the use of the RSASSA-PKCS1-V1_5 digital
signature algorithm as defined in Section 8.2 of RFC 3447 [RFC3447]
(commonly known as PKCS #1), using SHA-256, SHA-384, or SHA-512 [SHS]
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as the hash functions. The "alg" (algorithm) header parameter values
"RS256", "RS384", and "RS512" are used in the JWS Header to indicate
that the Encoded JWS Signature contains a base64url encoded RSASSA-
PKCS1-V1_5 digital signature using the respective hash function.
A key of size 2048 bits or larger MUST be used with these algorithms.
The RSASSA-PKCS1-V1_5 SHA-256 digital signature is generated as
follows:
1. Generate a digital signature of the octets of the ASCII
representation of the JWS Signing Input using RSASSA-PKCS1-V1_5-
SIGN and the SHA-256 hash function with the desired private key.
The output will be an octet sequence.
2. Base64url encode the resulting octet sequence.
The output is the Encoded JWS Signature for that JWS.
The RSASSA-PKCS1-V1_5 SHA-256 digital signature for a JWS is
validated as follows:
1. Take the Encoded JWS Signature and base64url decode it into an
octet sequence. If decoding fails, the JWS MUST be rejected.
2. Submit the octets of the ASCII representation of the JWS Signing
Input and the public key corresponding to the private key used by
the signer to the RSASSA-PKCS1-V1_5-VERIFY algorithm using SHA-
256 as the hash function.
3. If the validation fails, the JWS MUST be rejected.
Signing with the RSASSA-PKCS1-V1_5 SHA-384 and RSASSA-PKCS1-V1_5 SHA-
512 algorithms is performed identically to the procedure for RSASSA-
PKCS1-V1_5 SHA-256 - just using the corresponding hash algorithm with
correspondingly larger result values: 384 bits for RSASSA-PKCS1-V1_5
SHA-384 and 512 bits for RSASSA-PKCS1-V1_5 SHA-512.
An example using this algorithm is shown in Appendix A.2 of [JWS].
3.4. Digital Signature with ECDSA P-256 SHA-256, ECDSA P-384 SHA-384, or ECDSA P-521 SHA-512
The Elliptic Curve Digital Signature Algorithm (ECDSA) [DSS] provides
for the use of Elliptic Curve cryptography, which is able to provide
equivalent security to RSA cryptography but using shorter key sizes
and with greater processing speed. This means that ECDSA digital
signatures will be substantially smaller in terms of length than
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equivalently strong RSA digital signatures.
This specification defines the use of ECDSA with the P-256 curve and
the SHA-256 cryptographic hash function, ECDSA with the P-384 curve
and the SHA-384 hash function, and ECDSA with the P-521 curve and the
SHA-512 hash function. The P-256, P-384, and P-521 curves are
defined in [DSS]. The "alg" (algorithm) header parameter values
"ES256", "ES384", and "ES512" are used in the JWS Header to indicate
that the Encoded JWS Signature contains a base64url encoded ECDSA
P-256 SHA-256, ECDSA P-384 SHA-384, or ECDSA P-521 SHA-512 digital
signature, respectively.
The ECDSA P-256 SHA-256 digital signature is generated as follows:
1. Generate a digital signature of the octets of the ASCII
representation of the JWS Signing Input using ECDSA P-256 SHA-256
with the desired private key. The output will be the pair (R,
S), where R and S are 256 bit unsigned integers.
2. Turn R and S into octet sequences in big endian order, with each
array being be 32 octets long. The array representations MUST
NOT be shortened to omit any leading zero octets contained in the
values.
3. Concatenate the two octet sequences in the order R and then S.
(Note that many ECDSA implementations will directly produce this
concatenation as their output.)
4. Base64url encode the resulting 64 octet sequence.
The output is the Encoded JWS Signature for the JWS.
The ECDSA P-256 SHA-256 digital signature for a JWS is validated as
follows:
1. Take the Encoded JWS Signature and base64url decode it into an
octet sequence. If decoding fails, the JWS MUST be rejected.
2. The output of the base64url decoding MUST be a 64 octet sequence.
If decoding does not result in a 64 octet sequence, the JWS MUST
be rejected.
3. Split the 64 octet sequence into two 32 octet sequences. The
first array will be R and the second S (with both being in big
endian octet order).
4. Submit the octets of the ASCII representation of the JWS Signing
Input R, S and the public key (x, y) to the ECDSA P-256 SHA-256
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validator.
5. If the validation fails, the JWS MUST be rejected.
Note that ECDSA digital signature contains a value referred to as K,
which is a random number generated for each digital signature
instance. This means that two ECDSA digital signatures using exactly
the same input parameters will output different signature values
because their K values will be different. A consequence of this is
that one cannot validate an ECDSA signature by recomputing the
signature and comparing the results.
Signing with the ECDSA P-384 SHA-384 and ECDSA P-521 SHA-512
algorithms is performed identically to the procedure for ECDSA P-256
SHA-256 - just using the corresponding hash algorithm with
correspondingly larger result values. For ECDSA P-384 SHA-384, R and
S will be 384 bits each, resulting in a 96 octet sequence. For ECDSA
P-521 SHA-512, R and S will be 521 bits each, resulting in a 132
octet sequence.
Examples using these algorithms are shown in Appendices A.3 and A.4
of [JWS].
3.5. Digital Signature with RSASSA-PSS and SHA-256 or SHA-512
This section defines the use of the RSASSA-PSS digital signature
algorithm as defined in Section 8.1 of RFC 3447 [RFC3447] with the
MGF1 mask generation function, always using the same hash function
for both the RSASSA-PSS hash function and the MGF1 hash function.
Use of both SHA-256 and SHA-512 as these hash functions is defined.
All other algorithm parameters use the defaults specified in Section
A.2.3 of RFC 3447. The "alg" (algorithm) header parameter values
"PS256" and "PS512" is used in the JWS Header to indicate that the
Encoded JWS Signature contains a base64url encoded RSASSA-PSS digital
signature using the respective hash function in both roles.
A key of size 2048 bits or larger MUST be used with this algorithm.
The RSASSA-PSS SHA-256 digital signature is generated as follows:
1. Generate a digital signature of the octets of the ASCII
representation of the JWS Signing Input using RSASSA-PSS-SIGN,
the SHA-256 hash function, and the MGF1 mask generation function
with SHA-256 with the desired private key. The output will be an
octet sequence.
2. Base64url encode the resulting octet sequence.
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The output is the Encoded JWS Signature for that JWS.
The RSASSA-PSS SHA-256 digital signature for a JWS is validated as
follows:
1. Take the Encoded JWS Signature and base64url decode it into an
octet sequence. If decoding fails, the JWS MUST be rejected.
2. Submit the octets of the ASCII representation of the JWS Signing
Input and the public key corresponding to the private key used by
the signer to the RSASSA-PSS-VERIFY algorithm using SHA-256 as
the hash function and using MGF1 as the mask generation function
with SHA-256.
3. If the validation fails, the JWS MUST be rejected.
Signing with the RSASSA-PSS SHA-512 algorithm is performed
identically to the procedure for RSASSA-PSS SHA-256 - just using the
alternative hash algorithm in both roles.
3.6. Using the Algorithm "none"
JWSs MAY also be created that do not provide integrity protection.
Such a JWS is called a "Plaintext JWS". Plaintext JWSs MUST use the
"alg" value "none", and are formatted identically to other JWSs, but
with the empty string for its JWS Signature value.
3.7. Additional Digital Signature/MAC Algorithms and Parameters
Additional algorithms MAY be used to protect JWSs with corresponding
"alg" (algorithm) header parameter values being defined to refer to
them. New "alg" header parameter values SHOULD either be registered
in the IANA JSON Web Signature and Encryption Algorithms registry
Section 6.1 or be a value that contains a Collision Resistant
Namespace. In particular, it is permissible to use the algorithm
identifiers defined in XML DSIG [RFC3275], XML DSIG 2.0
[W3C.CR-xmldsig-core2-20120124], and related specifications as "alg"
values.
As indicated by the common registry, JWSs and JWEs share a common
"alg" value space. The values used by the two specifications MUST be
distinct, as the "alg" value can be used to determine whether the
object is a JWS or JWE.
Likewise, additional reserved Header Parameter Names can be defined
via the IANA JSON Web Signature and Encryption Header Parameters
registry [JWS]. As indicated by the common registry, JWSs and JWEs
share a common header parameter space; when a parameter is used by
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An example using this algorithm is shown in Appendix A.1 of [JWE].
4.5. Key Wrapping with AES Key Wrap
This section defines the specifics of encrypting a JWE CEK with the
Advanced Encryption Standard (AES) Key Wrap Algorithm [RFC3394] using
the default initial value specified in Section 2.2.3.1 using 128 or
256 bit keys. The "alg" header parameter values "A128KW" or "A256KW"
are used in this case.
An example using this algorithm is shown in Appendix A.3 of [JWE].
4.6. Direct Encryption with a Shared Symmetric Key
This section defines the specifics of directly performing symmetric
key encryption without performing a key wrapping step. In this case,
the shared symmetric key is used directly as the Content Encryption
Key (CEK) value for the "enc" algorithm. An empty octet sequence is
used as the JWE Encrypted Key value. The "alg" header parameter
value "dir" is used in this case.
4.7. Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static
(ECDH-ES)
This section defines the specifics of key agreement with Elliptic
Curve Diffie-Hellman Ephemeral Static [RFC6090], and using the Concat
KDF, as defined in Section 5.8.1 of [NIST.800-56A]. The key
agreement result can be used in one of two ways:
1. directly as the Content Encryption Key (CEK) for the "enc"
algorithm, in the Direct Key Agreement mode, or
2. as a symmetric key used to wrap the CEK with either the "A128KW"
or "A256KW" algorithms, in the Key Agreement with Key Wrapping
mode.
The "alg" header parameter value "ECDH-ES" is used in the Direct Key
Agreement mode and the values "ECDH-ES+A128KW" and "ECDH-ES+A256KW"
are used in the Key Agreement with Key Wrapping mode.
In the Direct Key Agreement case, the output of the Concat KDF MUST
be a key of the same length as that used by the "enc" algorithm; in
this case, the empty octet sequence is used as the JWE Encrypted Key
value. In the Key Agreement with Key Wrapping case, the output of
the Concat KDF MUST be a key of the length needed for the specified
key wrapping algorithm, either 128 or 256 bits respectively.
A new "epk" (ephemeral public key) value MUST be generated for each
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key agreement transaction.
4.7.1. Key Derivation for "ECDH-ES"
The key derivation process derives the agreed upon key from the
shared secret Z established through the ECDH algorithm, per Section6.2.2.2 of [NIST.800-56A].
Key derivation is performed using the Concat KDF, as defined in
Section 5.8.1 of [NIST.800-56A], where the Digest Method is SHA-256.
The Concat KDF parameters are set as follows:
Z This is set to the representation of the shared secret Z as an
octet sequence.
keydatalen This is set to the number of bits in the desired output
key. For "ECDH-ES", this is length of the key used by the "enc"
algorithm. For "ECDH-ES+A128KW", and "ECDH-ES+A256KW", this is
128 and 256, respectively.
AlgorithmID This is set to the octets of the UTF-8 representation of
the "alg" header parameter value.
PartyUInfo PartyUInfo contains a random data value provided by the
sender. If provided, this value MUST contain at least 512 bits
and a unique value SHOULD be used for each recipient. Use of
PartyUInfo is OPTIONAL when a different ephemeral key is used for
each key agreement transaction. The PartyUInfo value is of the
form Datalen || Data, where Data is a variable-length string of
zero or more octets, and Datalen is a fixed-length, big endian 32
bit counter that indicates the length (in octets) of Data, with ||
being concatenation. If an "apu" (agreement PartyUInfo) header
parameter is present, Data is set to the result of base64url
decoding the "apu" value and Datalen is set to the number of
octets in Data. Otherwise, Datalen is set to 0 and Data is set to
the empty octet sequence.
PartyVInfo This is set to the empty octet sequence.
SuppPubInfo This is set to the keydatalen represented as a 32 bit
big endian integer.
SuppPrivInfo This is set to the empty octet sequence.
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This section defines a family of authenticated encryption algorithms
built using a composition of Advanced Encryption Standard (AES) in
Cipher Block Chaining (CBC) mode with PKCS #5 padding [AES]
[NIST.800-38A] operations and HMAC [RFC2104] [SHS] operations. This
algorithm family is called AES_CBC_HMAC_SHA2. It also defines two
instances of this family, one using 128 bit CBC keys and HMAC SHA-256
and the other using 256 bit CBC keys and HMAC SHA-512. Test cases
for these algorithms can be found in Appendix C.
These algorithms are based upon Authenticated Encryption with AES-CBC
and HMAC-SHA [I-D.mcgrew-aead-aes-cbc-hmac-sha2], performing the same
cryptographic computations, but with the Initialization Vector and
Authentication Tag values remaining separate, rather than being
concatenated with the Ciphertext value in the output representation.
This algorithm family is a generalization of the algorithm family in
[I-D.mcgrew-aead-aes-cbc-hmac-sha2], and can be used to implement
those algorithms.
4.8.1. Conventions Used in Defining AES_CBC_HMAC_SHA2
We use the following notational conventions.
CBC-PKCS5-ENC(X, P) denotes the AES CBC encryption of P using PKCS
#5 padding using the cipher with the key X.
MAC(Y, M) denotes the application of the Message Authentication
Code (MAC) to the message M, using the key Y.
The concatenation of two octet strings A and B is denoted as
A || B.
4.8.2. Generic AES_CBC_HMAC_SHA2 Algorithm
This section defines AES_CBC_HMAC_SHA2 in a manner that is
independent of the AES CBC key size or hash function to be used.
Section 4.8.2.1 and Section 4.8.2.2 define the generic encryption and
decryption algorithms. Section 4.8.3 and Section 4.8.4 define
instances of AES_CBC_HMAC_SHA2 that specify those details.
4.8.2.1. AES_CBC_HMAC_SHA2 Encryption
The authenticated encryption algorithm takes as input four octet
strings: a secret key K, a plaintext P, associated data A, and an
initialization vector IV. The authenticated ciphertext value E and
the authentication tag value T are provided as outputs. The data in
the plaintext are encrypted and authenticated, and the associated
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data are authenticated, but not encrypted.
The encryption process is as follows, or uses an equivalent set of
steps:
1. The secondary keys MAC_KEY and ENC_KEY are generated from the
input key K as follows. Each of these two keys is an octet
string.
MAC_KEY consists of the initial MAC_KEY_LEN octets of K, in
order.
ENC_KEY consists of the final ENC_KEY_LEN octets of K, in
order.
Here we denote the number of octets in the MAC_KEY as
MAC_KEY_LEN, and the number of octets in ENC_KEY as ENC_KEY_LEN;
the values of these parameters are specified by the AEAD
algorithms (in Section 4.8.3 and Section 4.8.4). The number of
octets in the input key K is the sum of MAC_KEY_LEN and
ENC_KEY_LEN. When generating the secondary keys from K, MAC_KEY
and ENC_KEY MUST NOT overlap. Note that the MAC key comes before
the encryption key in the input key K; this is in the opposite
order of the algorithm names in the identifier
"AES_CBC_HMAC_SHA2".
2. The Initialization Vector (IV) used is a 128 bit value generated
randomly or pseudorandomly for use in the cipher.
3. The plaintext is CBC encrypted using PKCS #5 padding using
ENC_KEY as the key, and the IV. We denote the ciphertext output
from this step as E.
4. The octet string AL is equal to the number of bits in A expressed
as a 64-bit unsigned integer in network byte order.
5. A message authentication tag T is computed by applying HMAC
[RFC2104] to the following data, in order:
the associated data A,
the initialization vector IV,
the ciphertext E computed in the previous step, and
the octet string AL defined above.
The string MAC_KEY is used as the MAC key. We denote the output
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of the MAC computed in this step as M. The first T_LEN bits of M
are used as T.
6. The Ciphertext E and the Authentication Tag T are returned as the
outputs of the authenticated encryption.
The encryption process can be illustrated as follows. Here K, P, A,
IV, and E denote the key, plaintext, associated data, initialization
vector, and ciphertext, respectively.
MAC_KEY = initial MAC_KEY_LEN bytes of K,
ENC_KEY = final ENC_KEY_LEN bytes of K,
E = CBC-PKCS5-ENC(ENC_KEY, P),
M = MAC(MAC_KEY, A || IV || E || AL),
T = initial T_LEN bytes of M.
4.8.2.2. AES_CBC_HMAC_SHA2 Decryption
The authenticated decryption operation has four inputs: K, A, E, and
T as defined above. It has only a single output, either a plaintext
value P or a special symbol FAIL that indicates that the inputs are
not authentic. The authenticated decryption algorithm is as follows,
or uses an equivalent set of steps:
1. The secondary keys MAC_KEY and ENC_KEY are generated from the
input key K as in Step 1 of Section 4.8.2.1.
2. The integrity and authenticity of A and E are checked by
computing an HMAC with the inputs as in Step 5 of
Section 4.8.2.1. The value T, from the previous step, is
compared to the first MAC_KEY length bits of the HMAC output. If
those values are identical, then A and E are considered valid,
and processing is continued. Otherwise, all of the data used in
the MAC validation are discarded, and the AEAD decryption
operation returns an indication that it failed, and the operation
halts. (But see Section 10 of [JWE] for security considerations
on thwarting timing attacks.)
3. The value E is decrypted and the PKCS #5 padding is removed. The
value IV is used as the initialization vector. The value ENC_KEY
is used as the decryption key.
4. The plaintext value is returned.
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Internet-Draft JSON Web Algorithms (JWA) May 20134.8.3. AES_128_CBC_HMAC_SHA_256
This algorithm is a concrete instantiation of the generic
AES_CBC_HMAC_SHA2 algorithm above. It uses the HMAC message
authentication code [RFC2104] with the SHA-256 hash function [SHS] to
provide message authentication, with the HMAC output truncated to 128
bits, corresponding to the HMAC-SHA-256-128 algorithm defined in
[RFC4868]. For encryption, it uses AES in the cipher block chaining
(CBC) mode of operation as defined in Section 6.2 of [NIST.800-38A],
with PKCS #5 padding.
The input key K is 32 octets long.
The AES CBC IV is 16 octets long. ENC_KEY_LEN is 16 octets.
The SHA-256 hash algorithm is used in HMAC. MAC_KEY_LEN is 16
octets. The HMAC-SHA-256 output is truncated to T_LEN=16 octets, by
stripping off the final 16 octets.
4.8.4. AES_256_CBC_HMAC_SHA_512
AES_256_CBC_HMAC_SHA_512 is based on AES_128_CBC_HMAC_SHA_256, but
with the following differences:
A 256 bit AES CBC key is used instead of 128.
SHA-512 is used in HMAC instead of SHA-256.
ENC_KEY_LEN is 32 octets.
MAC_KEY_LEN is 32 octets.
The length of the input key K is 64 octets.
The HMAC SHA-512 value is truncated to T_LEN=32 octets instead of
16 octets.
4.8.5. Plaintext Encryption with AES_CBC_HMAC_SHA2
The algorithm value "A128CBC-HS256" is used as the "alg" value when
using AES_128_CBC_HMAC_SHA_256 with JWE. The algorithm value
"A256CBC-HS512" is used as the "alg" value when using
AES_256_CBC_HMAC_SHA_512 with JWE. The Additional Authenticated Data
value used is the octets of the ASCII representation of the Encoded
JWE Header value. The JWE Initialization Vector value used is the IV
value.
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Internet-Draft JSON Web Algorithms (JWA) May 20134.9. Plaintext Encryption with AES GCM
This section defines the specifics of encrypting the JWE Plaintext
with Advanced Encryption Standard (AES) in Galois/Counter Mode (GCM)
[AES] [NIST.800-38D] using 128 or 256 bit keys. The "enc" header
parameter values "A128GCM" or "A256GCM" are used in this case.
The CEK is used as the encryption key.
Use of an initialization vector of size 96 bits is REQUIRED with this
algorithm.
The Additional Authenticated Data value used is the octets of the
ASCII representation of the Encoded JWE Header value.
The requested size of the Authentication Tag output MUST be 128 bits,
regardless of the key size.
The JWE Authentication Tag is set to be the Authentication Tag value
produced by the encryption. During decryption, the received JWE
Authentication Tag is used as the Authentication Tag value.
An example using this algorithm is shown in Appendix A.1 of [JWE].
4.10. Additional Encryption Algorithms and Parameters
Additional algorithms MAY be used to protect JWEs with corresponding
"alg" (algorithm) and "enc" (encryption method) header parameter
values being defined to refer to them. New "alg" and "enc" header
parameter values SHOULD either be registered in the IANA JSON Web
Signature and Encryption Algorithms registry Section 6.1 or be a
value that contains a Collision Resistant Namespace. In particular,
it is permissible to use the algorithm identifiers defined in XML
Encryption [W3C.REC-xmlenc-core-20021210], XML Encryption 1.1
[W3C.CR-xmlenc-core1-20120313], and related specifications as "alg"
and "enc" values.
As indicated by the common registry, JWSs and JWEs share a common
"alg" value space. The values used by the two specifications MUST be
distinct, as the "alg" value can be used to determine whether the
object is a JWS or JWE.
Likewise, additional reserved Header Parameter Names can be defined
via the IANA JSON Web Signature and Encryption Header Parameters
registry [JWS]. As indicated by the common registry, JWSs and JWEs
share a common header parameter space; when a parameter is used by
both specifications, its usage must be compatible between the
specifications.
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Internet-Draft JSON Web Algorithms (JWA) May 20135. Cryptographic Algorithms for JWK
A JSON Web Key (JWK) [JWK] is a JavaScript Object Notation (JSON)
[RFC4627] data structure that represents a cryptographic key. A JSON
Web Key Set (JWK Set) is a JSON data structure for representing a set
of JWKs. This section specifies a set of key types to be used for
those keys and the key type specific parameters for representing
those keys. Parameters are defined for public, private, and
symmetric keys.
5.1. "kty" (Key Type) Parameter Values for JWK
The table below is the set of "kty" (key type) parameter values that
are defined by this specification for use in JWKs.
+-------------+----------------------------------+------------------+
| kty | Key Type | Implementation |
| Parameter | | Requirements |
| Value | | |
+-------------+----------------------------------+------------------+
| EC | Elliptic Curve [DSS] key type | RECOMMENDED+ |
| RSA | RSA [RFC3447] key type | REQUIRED |
| oct | Octet sequence key type (used to | RECOMMENDED+ |
| | represent symmetric keys) | |
+-------------+----------------------------------+------------------+
All the names are short because a core goal of JWK is for the
representations to be compact. However, there is no a priori length
restriction on "kty" values.
The use of "+" in the Implementation Requirements indicates that the
requirement strength is likely to be increased in a future version of
the specification.
5.2. JWK Parameters for Elliptic Curve Keys
JWKs can represent Elliptic Curve [DSS] keys. In this case, the
"kty" member value MUST be "EC".
5.2.1. JWK Parameters for Elliptic Curve Public Keys
These members MUST be present for Elliptic Curve public keys:
5.2.1.1. "crv" (Curve) Parameter
The "crv" (curve) member identifies the cryptographic curve used with
the key. Curve values from [DSS] used by this specification are:
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o "P-256"
o "P-384"
o "P-521"
Additional "crv" values MAY be used, provided they are understood by
implementations using that Elliptic Curve key. The "crv" value is a
case sensitive string.
5.2.1.2. "x" (X Coordinate) Parameter
The "x" (x coordinate) member contains the x coordinate for the
elliptic curve point. It is represented as the base64url encoding of
the coordinate's big endian representation as an octet sequence. The
array representation MUST NOT be shortened to omit any leading zero
octets contained in the value. For instance, when representing 521
bit integers, the octet sequence to be base64url encoded MUST contain
66 octets, including any leading zero octets.
5.2.1.3. "y" (Y Coordinate) Parameter
The "y" (y coordinate) member contains the y coordinate for the
elliptic curve point. It is represented as the base64url encoding of
the coordinate's big endian representation as an octet sequence. The
array representation MUST NOT be shortened to omit any leading zero
octets contained in the value. For instance, when representing 521
bit integers, the octet sequence to be base64url encoded MUST contain
66 octets, including any leading zero octets.
5.2.2. JWK Parameters for Elliptic Curve Private Keys
In addition to the members used to represent Elliptic Curve public
keys, the following member MUST be present to represent Elliptic
Curve private keys:
5.2.2.1. "d" (ECC Private Key) Parameter
The "d" (ECC private key) member contains the Elliptic Curve private
key value. It is represented as the base64url encoding of the
value's unsigned big endian representation as an octet sequence. The
array representation MUST NOT be shortened to omit any leading zero
octets. For instance, when representing 521 bit integers, the octet
sequence to be base64url encoded MUST contain 66 octets, including
any leading zero octets.
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Internet-Draft JSON Web Algorithms (JWA) May 20135.3. JWK Parameters for RSA Keys
JWKs can represent RSA [RFC3447] keys. In this case, the "kty"
member value MUST be "RSA".
5.3.1. JWK Parameters for RSA Public Keys
These members MUST be present for RSA public keys:
5.3.1.1. "n" (Modulus) Parameter
The "n" (modulus) member contains the modulus value for the RSA
public key. It is represented as the base64url encoding of the
value's unsigned big endian representation as an octet sequence. The
array representation MUST NOT be shortened to omit any leading zero
octets. For instance, when representing 2048 bit integers, the octet
sequence to be base64url encoded MUST contain 256 octets, including
any leading zero octets.
5.3.1.2. "e" (Exponent) Parameter
The "e" (exponent) member contains the exponent value for the RSA
public key. It is represented as the base64url encoding of the
value's unsigned big endian representation as an octet sequence. The
array representation MUST utilize the minimum number of octets to
represent the value. For instance, when representing the value
65537, the octet sequence to be base64url encoded MUST consist of the
three octets [1, 0, 1].
5.3.2. JWK Parameters for RSA Private Keys
In addition to the members used to represent RSA public keys, the
following members are used to represent RSA private keys. All are
REQUIRED for RSA private keys except for "oth", which is sometimes
REQUIRED and sometimes MUST NOT be present, as described below.
5.3.2.1. "d" (Private Exponent) Parameter
The "d" (private exponent) member contains the private exponent value
for the RSA private key. It is represented as the base64url encoding
of the value's unsigned big endian representation as an octet
sequence. The array representation MUST NOT be shortened to omit any
leading zero octets. For instance, when representing 2048 bit
integers, the octet sequence to be base64url encoded MUST contain 256
octets, including any leading zero octets.
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Internet-Draft JSON Web Algorithms (JWA) May 20135.3.2.2. "p" (First Prime Factor) Parameter
The "p" (first prime factor) member contains the first prime factor,
a positive integer. It is represented as the base64url encoding of
the value's unsigned big endian representation as an octet sequence.
5.3.2.3. "q" (Second Prime Factor) Parameter
The "q" (second prime factor) member contains the second prime
factor, a positive integer. It is represented as the base64url
encoding of the value's unsigned big endian representation as an
octet sequence.
5.3.2.4. "dp" (First Factor CRT Exponent) Parameter
The "dp" (first factor CRT exponent) member contains the Chinese
Remainder Theorem (CRT) exponent of the first factor, a positive
integer. It is represented as the base64url encoding of the value's
unsigned big endian representation as an octet sequence.
5.3.2.5. "dq" (Second Factor CRT Exponent) Parameter
The "dq" (second factor CRT exponent) member contains the Chinese
Remainder Theorem (CRT) exponent of the second factor, a positive
integer. It is represented as the base64url encoding of the value's
unsigned big endian representation as an octet sequence.
5.3.2.6. "qi" (First CRT Coefficient) Parameter
The "dp" (first CRT coefficient) member contains the Chinese
Remainder Theorem (CRT) coefficient of the second factor, a positive
integer. It is represented as the base64url encoding of the value's
unsigned big endian representation as an octet sequence.
5.3.2.7. "oth" (Other Primes Info) Parameter
The "oth" (other primes info) member contains an array of information
about any third and subsequent primes, should they exist. When only
two primes have been used (the normal case), this parameter MUST be
omitted. When three or more primes have been used, the number of
array elements MUST be the number of primes used minus two. Each
array element MUST be an object with the following members:
5.3.2.7.1. "r" (Prime Factor)
The "r" (prime factor) parameter within an "oth" array member
represents the value of a subsequent prime factor, a positive
integer. It is represented as the base64url encoding of the value's
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unsigned big endian representation as an octet sequence.
5.3.2.7.2. "d" (Factor CRT Exponent)
The "d" (Factor CRT Exponent) parameter within an "oth" array member
represents the CRT exponent of the corresponding prime factor, a
positive integer. It is represented as the base64url encoding of the
value's unsigned big endian representation as an octet sequence.
5.3.2.7.3. "t" (Factor CRT Coefficient)
The "t" (factor CRT coefficient) parameter within an "oth" array
member represents the CRT coefficient of the corresponding prime
factor, a positive integer. It is represented as the base64url
encoding of the value's unsigned big endian representation as an
octet sequence.
5.3.3. JWK Parameters for Symmetric Keys
When the JWK "kty" member value is "oct" (octet sequence), the
following member is used to represent a symmetric key (or another key
whose value is a single octet sequence):
5.3.3.1. "k" (Key Value) Parameter
The "k" (key value) member contains the value of the symmetric (or
other single-valued) key. It is represented as the base64url
encoding of the octet sequence containing the key value.
5.4. Additional Key Types and Parameters
Keys using additional key types can be represented using JWK data
structures with corresponding "kty" (key type) parameter values being
defined to refer to them. New "kty" parameter values SHOULD either
be registered in the IANA JSON Web Key Types registry Section 6.2 or
be a value that contains a Collision Resistant Namespace.
Likewise, parameters for representing keys for additional key types
or additional key properties SHOULD either be registered in the IANA
JSON Web Key Parameters registry [JWK] or be a value that contains a
Collision Resistant Namespace.
6. IANA Considerations
The following registration procedure is used for all the registries
established by this specification.
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Values are registered with a Specification Required [RFC5226] after a
two-week review period on the [TBD]@ietf.org mailing list, on the
advice of one or more Designated Experts. However, to allow for the
allocation of values prior to publication, the Designated Expert(s)
may approve registration once they are satisfied that such a
specification will be published.
Registration requests must be sent to the [TBD]@ietf.org mailing list
for review and comment, with an appropriate subject (e.g., "Request
for access token type: example"). [[ Note to RFC-EDITOR: The name of
the mailing list should be determined in consultation with the IESG
and IANA. Suggested name: jose-reg-review. ]]
Within the review period, the Designated Expert(s) will either
approve or deny the registration request, communicating this decision
to the review list and IANA. Denials should include an explanation
and, if applicable, suggestions as to how to make the request
successful.
IANA must only accept registry updates from the Designated Expert(s)
and should direct all requests for registration to the review mailing
list.
6.1. JSON Web Signature and Encryption Algorithms Registry
This specification establishes the IANA JSON Web Signature and
Encryption Algorithms registry for values of the JWS and JWE "alg"
(algorithm) and "enc" (encryption method) header parameters. The
registry records the algorithm name, the algorithm usage locations
from the set "alg" and "enc", implementation requirements, and a
reference to the specification that defines it. The same algorithm
name MAY be registered multiple times, provided that the sets of
usage locations are disjoint. The implementation requirements of an
algorithm MAY be changed over time by the Designated Experts(s) as
the cryptographic landscape evolves, for instance, to change the
status of an algorithm to DEPRECATED, or to change the status of an
algorithm from OPTIONAL to RECOMMENDED or REQUIRED.
6.1.1. Template
Algorithm Name:
The name requested (e.g., "example"). This name is case
sensitive. Names that match other registered names in a case
insensitive manner SHOULD NOT be accepted.
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Algorithm Usage Location(s):
The algorithm usage, which must be one or more of the values "alg"
or "enc".
Implementation Requirements:
The algorithm implementation requirements, which must be one the
words REQUIRED, RECOMMENDED, OPTIONAL, or DEPRECATED. Optionally,
the word can be followed by a "+" or "-". The use of "+"
indicates that the requirement strength is likely to be increased
in a future version of the specification. The use of "-"
indicates that the requirement strength is likely to be decreased
in a future version of the specification.
Change Controller:
For Standards Track RFCs, state "IETF". For others, give the name
of the responsible party. Other details (e.g., postal address,
email address, home page URI) may also be included.
Specification Document(s):
Reference to the document(s) that specify the parameter,
preferably including URI(s) that can be used to retrieve copies of
the document(s). An indication of the relevant sections may also
be included but is not required.
6.1.2. Initial Registry Contents
o Algorithm Name: "HS256"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: REQUIRED
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "HS384"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: OPTIONAL
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "HS512"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: OPTIONAL
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "RS256"
o Algorithm Usage Location(s): "alg"
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Change Controller:
For Standards Track RFCs, state "IETF". For others, give the name
of the responsible party. Other details (e.g., postal address,
email address, home page URI) may also be included.
Implementation Requirements:
The algorithm implementation requirements, which must be one the
words REQUIRED, RECOMMENDED, OPTIONAL, or DEPRECATED. Optionally,
the word can be followed by a "+" or "-". The use of "+"
indicates that the requirement strength is likely to be increased
in a future version of the specification. The use of "-"
indicates that the requirement strength is likely to be decreased
in a future version of the specification.
Specification Document(s):
Reference to the document(s) that specify the parameter,
preferably including URI(s) that can be used to retrieve copies of
the document(s). An indication of the relevant sections may also
be included but is not required.
6.2.2. Initial Registry Contents
o "kty" Parameter Value: "EC"
o Implementation Requirements: RECOMMENDED+
o Change Controller: IETF
o Specification Document(s): Section 5.1 of [[ this document ]]
o "kty" Parameter Value: "RSA"
o Implementation Requirements: REQUIRED
o Change Controller: IETF
o Specification Document(s): Section 5.1 of [[ this document ]]
o "kty" Parameter Value: "oct"
o Implementation Requirements: RECOMMENDED+
o Change Controller: IETF
o Specification Document(s): Section 5.1 of [[ this document ]]
6.3. JSON Web Key Parameters Registration
This specification registers the parameter names defined in Sections
5.2, 5.3, and 5.3.3 in the IANA JSON Web Key Parameters registry
[JWK].
6.3.1. Registry Contents
o Parameter Name: "crv"
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o Change Controller: IETF
o Specification Document(s): Section 5.3.2.4 of [[ this document ]]
o Parameter Name: "dq"
o Parameter Information Class: Private
o Change Controller: IETF
o Specification Document(s): Section 5.3.2.5 of [[ this document ]]
o Parameter Name: "qi"
o Parameter Information Class: Private
o Change Controller: IETF
o Specification Document(s): Section 5.3.2.6 of [[ this document ]]
o Parameter Name: "oth"
o Parameter Information Class: Private
o Change Controller: IETF
o Specification Document(s): Section 5.3.2.7 of [[ this document ]]
o Parameter Name: "k"
o Parameter Information Class: Private
o Change Controller: IETF
o Specification Document(s): Section 5.3.3.1 of [[ this document ]]
7. Security Considerations
All of the security issues faced by any cryptographic application
must be faced by a JWS/JWE/JWK agent. Among these issues are
protecting the user's private and symmetric keys, preventing various
attacks, and helping the user avoid mistakes such as inadvertently
encrypting a message for the wrong recipient. The entire list of
security considerations is beyond the scope of this document, but
some significant considerations are listed here.
The security considerations in [AES], [DSS], [JWE], [JWK], [JWS],
[NIST.800-38A], [NIST.800-38D], [NIST.800-56A], [RFC2104], [RFC3394],
[RFC3447], [RFC5116], [RFC6090], and [SHS] apply to this
specification.
Eventually the algorithms and/or key sizes currently described in
this specification will no longer be considered sufficiently secure
and will be removed. Therefore, implementers and deployments must be
prepared for this eventuality.
Algorithms of matching strengths should be used together whenever
possible. For instance, when AES Key Wrap is used with a given key
size, using the same key size is recommended when AES GCM is also
used.
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While Section 8 of RFC 3447 [RFC3447] explicitly calls for people not
to adopt RSASSA-PKCS-v1_5 for new applications and instead requests
that people transition to RSASSA-PSS, this specification does include
RSASSA-PKCS-v1_5, for interoperability reasons, because it commonly
implemented.
Keys used with RSAES-PKCS1-v1_5 must follow the constraints in
Section 7.2 of RFC 3447 [RFC3447]. In particular, keys with a low
public key exponent value must not be used.
Plaintext JWSs (JWSs that use the "alg" value "none") provide no
integrity protection. Thus, they must only be used in contexts where
the payload is secured by means other than a digital signature or MAC
value, or need not be secured.
Receiving agents that validate signatures and sending agents that
encrypt messages need to be cautious of cryptographic processing
usage when validating signatures and encrypting messages using keys
larger than those mandated in this specification. An attacker could
send certificates with keys that would result in excessive
cryptographic processing, for example, keys larger than those
mandated in this specification, which could swamp the processing
element. Agents that use such keys without first validating the
certificate to a trust anchor are advised to have some sort of
cryptographic resource management system to prevent such attacks.
8. References8.1. Normative References
[AES] National Institute of Standards and Technology (NIST),
"Advanced Encryption Standard (AES)", FIPS PUB 197,
November 2001.
[DSS] National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS PUB 186-3, June 2009.
[JWE] Jones, M., Rescorla, E., and J. Hildebrand, "JSON Web
Encryption (JWE)", draft-ietf-jose-json-web-encryption
(work in progress), May 2013.
[JWK] Jones, M., "JSON Web Key (JWK)",
draft-ietf-jose-json-web-key (work in progress), May 2013.
[JWS] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", draft-ietf-jose-json-web-signature (work
in progress), May 2013.
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Internet-Draft JSON Web Algorithms (JWA) May 2013Appendix D. Acknowledgements
Solutions for signing and encrypting JSON content were previously
explored by Magic Signatures [MagicSignatures], JSON Simple Sign
[JSS], Canvas Applications [CanvasApp], JSON Simple Encryption [JSE],
and JavaScript Message Security Format [I-D.rescorla-jsms], all of
which influenced this draft.
The Authenticated Encryption with AES-CBC and HMAC-SHA
[I-D.mcgrew-aead-aes-cbc-hmac-sha2] specification, upon which the
AES_CBC_HMAC_SHA2 algorithms are based, was written by David A.
McGrew and Kenny Paterson. The test cases for AES_CBC_HMAC_SHA2 are
based upon those for [I-D.mcgrew-aead-aes-cbc-hmac-sha2] by John
Foley.
This specification is the work of the JOSE Working Group, which
includes dozens of active and dedicated participants. In particular,
the following individuals contributed ideas, feedback, and wording
that influenced this specification:
Dirk Balfanz, Richard Barnes, John Bradley, Brian Campbell, Breno de
Medeiros, Yaron Y. Goland, Dick Hardt, Jeff Hodges, Edmund Jay, James
Manger, Tony Nadalin, Axel Nennker, John Panzer, Emmanuel Raviart,
Nat Sakimura, Jim Schaad, Hannes Tschofenig, and Sean Turner.
Jim Schaad and Karen O'Donoghue chaired the JOSE working group and
Sean Turner and Stephen Farrell served as Security area directors
during the creation of this specification.
Appendix E. Document History
[[ to be removed by the RFC editor before publication as an RFC ]]
-11
o Removed the Encrypted Key value from the AAD computation since it
is already effectively integrity protected by the encryption
process. The AAD value now only contains the representation of
the JWE Encrypted Header.
o Removed "apv" (agreement PartyVInfo) since it is no longer used.
o Added more information about the use of PartyUInfo during key
agreement.
o Use the keydatalen as the SuppPubInfo value for the Concat KDF
when doing key agreement, as RFC 2631 does.
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Internet-Draft JSON Web Algorithms (JWA) May 2013
o Added algorithm identifiers for RSASSA-PSS with SHA-256 and SHA-
512.
o Added a Parameter Information Class value to the JSON Web Key
Parameters registry, which registers whether the parameter conveys
public or private information.
-10
o Changed the JWE processing rules for multiple recipients so that a
single AAD value contains the header parameters and encrypted key
values for all the recipients, enabling AES GCM to be safely used
for multiple recipients.
-09
o Expanded the scope of the JWK parameters to include private and
symmetric key representations, as specified by
draft-jones-jose-json-private-and-symmetric-key-00.
o Changed term "JWS Secured Input" to "JWS Signing Input".
o Changed from using the term "byte" to "octet" when referring to 8
bit values.
o Specified that AES Key Wrap uses the default initial value
specified in Section 2.2.3.1 of RFC 3394. This addressed issue
#19.
o Added Key Management Mode definitions to terminology section and
used the defined terms to provide clearer key management
instructions. This addressed issue #5.
o Replaced "A128CBC+HS256" and "A256CBC+HS512" with "A128CBC-HS256"
and "A256CBC-HS512". The new algorithms perform the same
cryptographic computations as [I-D.mcgrew-aead-aes-cbc-hmac-sha2],
but with the Initialization Vector and Authentication Tag values
remaining separate from the Ciphertext value in the output
representation. Also deleted the header parameters "epu"
(encryption PartyUInfo) and "epv" (encryption PartyVInfo), since
they are no longer used.
o Changed from using the term "Integrity Value" to "Authentication
Tag".
-08
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Internet-Draft JSON Web Algorithms (JWA) May 2013
o Changed the name of the JWK key type parameter from "alg" to
"kty".
o Replaced uses of the term "AEAD" with "Authenticated Encryption",
since the term AEAD in the RFC 5116 sense implied the use of a
particular data representation, rather than just referring to the
class of algorithms that perform authenticated encryption with
associated data.
o Applied editorial improvements suggested by Jeff Hodges. Many of
these simplified the terminology used.
o Added seriesInfo information to Internet Draft references.
-07
o Added a data length prefix to PartyUInfo and PartyVInfo values.
o Changed the name of the JWK RSA modulus parameter from "mod" to
"n" and the name of the JWK RSA exponent parameter from "xpo" to
"e", so that the identifiers are the same as those used in RFC3447.
o Made several local editorial changes to clean up loose ends left
over from to the decision to only support block encryption methods
providing integrity.
-06
o Removed the "int" and "kdf" parameters and defined the new
composite Authenticated Encryption algorithms "A128CBC+HS256" and
"A256CBC+HS512" to replace the former uses of AES CBC, which
required the use of separate integrity and key derivation
functions.
o Included additional values in the Concat KDF calculation -- the
desired output size and the algorithm value, and optionally
PartyUInfo and PartyVInfo values. Added the optional header
parameters "apu" (agreement PartyUInfo), "apv" (agreement
PartyVInfo), "epu" (encryption PartyUInfo), and "epv" (encryption
PartyVInfo).
o Changed the name of the JWK RSA exponent parameter from "exp" to
"xpo" so as to allow the potential use of the name "exp" for a
future extension that might define an expiration parameter for
keys. (The "exp" name is already used for this purpose in the JWT
specification.)
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Internet-Draft JSON Web Algorithms (JWA) May 2013
o Applied changes made by the RFC Editor to RFC 6749's registry
language to this specification.
-05
o Support both direct encryption using a shared or agreed upon
symmetric key, and the use of a shared or agreed upon symmetric
key to key wrap the CMK. Specifically, added the "alg" values
"dir", "ECDH-ES+A128KW", and "ECDH-ES+A256KW" to finish filling in
this set of capabilities.
o Updated open issues.
-04
o Added text requiring that any leading zero bytes be retained in
base64url encoded key value representations for fixed-length
values.
o Added this language to Registration Templates: "This name is case
sensitive. Names that match other registered names in a case
insensitive manner SHOULD NOT be accepted."
o Described additional open issues.
o Applied editorial suggestions.
-03
o Always use a 128 bit "authentication tag" size for AES GCM,
regardless of the key size.
o Specified that use of a 128 bit IV is REQUIRED with AES CBC. It
was previously RECOMMENDED.
o Removed key size language for ECDSA algorithms, since the key size
is implied by the algorithm being used.
o Stated that the "int" key size must be the same as the hash output
size (and not larger, as was previously allowed) so that its size
is defined for key generation purposes.
o Added the "kdf" (key derivation function) header parameter to
provide crypto agility for key derivation. The default KDF
remains the Concat KDF with the SHA-256 digest function.
o Clarified that the "mod" and "exp" values are unsigned.
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Internet-Draft JSON Web Algorithms (JWA) May 2013
o Removed the use of "A128GCM" and "A256GCM" for key wrapping.
o Removed "A512KW" since it turns out that it's not a standard
algorithm.
o Clarified the relationship between "typ" header parameter values
and MIME types.
o Generalized language to refer to Message Authentication Codes
(MACs) rather than Hash-based Message Authentication Codes (HMACs)
unless in a context specific to HMAC algorithms.
o Established registries: JSON Web Signature and Encryption Header
Parameters, JSON Web Signature and Encryption Algorithms, JSON Web
Signature and Encryption "typ" Values, JSON Web Key Parameters,
and JSON Web Key Algorithm Families.
o Moved algorithm-specific definitions from JWK to JWA.
o Reformatted to give each member definition its own section
heading.
-01
o Moved definition of "alg":"none" for JWSs here from the JWT
specification since this functionality is likely to be useful in
more contexts that just for JWTs.
o Added Advanced Encryption Standard (AES) Key Wrap Algorithm using
512 bit keys ("A512KW").
o Added text "Alternatively, the Encoded JWS Signature MAY be
base64url decoded to produce the JWS Signature and this value can
be compared with the computed HMAC value, as this comparison
produces the same result as comparing the encoded values".
o Corrected the Magic Signatures reference.
o Made other editorial improvements suggested by JOSE working group
participants.
-00
o Created the initial IETF draft based upon
draft-jones-json-web-signature-04 and
draft-jones-json-web-encryption-02 with no normative changes.
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